It is known to spray slurries of hydrated lime into the discharging flue gases from coal powered furnaces or boilers, such as in electric power plants, for the purpose of capturing, reaction with, and removing sulfur dioxide from the gases prior to discharge to the atmosphere. To effectively scrub sulfur dioxide from such gases, it is necessary that the slurry be finely atomized into small liquid droplets. It also is desirable that spray particles be of such small size in order to enhance drying prior to impinging upon the flue duct work so as to prevent build-up and corrosion.
Vidusek U.S. Pat. No. 5,176,325 discloses a spray nozzle assembly which overcomes many of the problems of prior spraying systems in that the nozzle assembly of the patent is capable of effectively discharging a finely atomized slurry of hydrated lime with low air consumption requirements and with reduced wear to exposed surfaces of the nozzle. In some installations, however, lime and fly ash build up rather rapidly on the center portion of the exposed face of the nozzle tip and detrimentally affect the spraying action. Attempts to solve the build-up problem by shrouding the external portion of the tip or by directing a stream of shielding air around the tip are relatively expensive and have met with only limited success.